1. Field of the Invention
The present invention relates to a retractable photographing (imaging) lens (retractable lens barrel) in which a part of a plurality of optical elements constituting an imaging optical system (photographing optical system) is retracted to a radially-retracted position deviating from the optical axis of the imaging optical system when the photographing lens is in a retracted state.
2. Description of the Related Art
Miniaturization of cameras has been in increasing demand. Above all, further miniaturization of retractable photographing lenses, specifically the length thereof in a non-operating state (retracted state), has been in strong demand. To meet such demands, the inventors of the present invention have proposed a retractable photographing lens disclosed in U.S. Pat. No. 6,978,089 (U.S. patent application Ser. No. 10/368,342) in which an optical element (displaceable element) of an imaging optical system is retracted to a radially-retracted position deviating from the optical axis of the imaging optical system (i.e., displaced from the optical axis of the imaging optical system), and at the same time, the optical element (together with other optical elements of the imaging optical system) is moved toward a picture plane when the photographing lens is fully retracted. More specifically, a linearly advancing/retracting member is supported by a linear guide member to be movable along the optical axis of the imaging optical system between an operating position and a retracted position, and the displaceable element is supported by the linearly advancing/retracting member to be movable between an on-axis position in which the displaceable element is positioned on the optical axis of the imaging optical system and an off-axis displaced position in which the displaceable element is displaced from the optical axis of the imaging optical system when the linearly advancing/retracting member is in the operating position and the retracted position, respectively.
Conventionally, a plurality of key projections for guiding the linearly advancing/retracting member in an optical axis direction are arranged on the linear guide member at intervals in the circumferential direction, and the displaceable element is accommodated in between the plurality of key projections when the linearly advancing/retracting member is in the retracted position. However, in this conventional structure, the efficiency of space utilization for retracting the displaceable element (especially in a circumferential direction) is low, which becomes an obstacle to miniaturization of the photographing lens.